memory speed

I was told to upgrade to 2 16 GB DDR4 for my Dell OptiPlex 7040 SFF
Device Name DESKTOP-
Processor Intel(R) Core(TM) i5-6500 CPU @ 3.20GHz   3.19 GHz
Installed RAM 16.0 GB (15.9 GB usable)
Storage 477 GB SSD SATA SSD
Graphics Card Intel(R) HD Graphics 530 (128 MB)
Device ID 60DC93AB-0EB7-43C7-8ED7-009378E48833
Product ID 00330-80000-00000-AA220
System Type 64-bit operating system, x64-based processor
Pen and touch No pen or touch input is available for this display

i am not sure of the speed that memory slots take of the 16 Gb DDR4 needs to be?